X-rays are produced by a refractory material, generally tungsten or an alloy made up mainly of tungsten, under the effect of an incident beam of electrons that is directed towards and bombards locally said material.
Commonly, the refractory material takes the form of a target coating formed on a disc made of another material and extending over an annular zone of the disc, this assembly being called an anode. This anode is mounted on a rotated shaft, such that the incident beam of electrons sweeps an annular track across the annular target coating made of a refractory material.
Generally, the speeds of rotation of such anodes may reach about 10,000 rotations per minute. The temperature at the point of impact of the electrons may reach 2000° C., the temperature of the anode, in its bulk, generally stabilizing at about 1300° C.
Such operation generates high thermomechanical stresses that gradually degrade the target coating made of a refractory material, more particularly in the scanned annular zone or track, possibly consisting in enlargement of the grains of the refractory material, in the appearance of microcracks and/or in erosion of the refractory material. Such degradation leads to a degradation of the power of the x-rays and to an increase in the spatial dispersion of the x-rays.
On account of the cost of the materials forming the disc, generally a molybdenum/titanium/zirconium (TZM) alloy, a graphite or a carbon/carbon composite, and the cost of manufacturing such a disc, it would seem to be desirable to repair damaged anodes. To this end, a number of solutions have already been proposed.
U.S. Pat. No. 5,013,274 (incorporated by reference) describes a method for repairing anodes, in which holes resulting from damage to the target coating made of a refractory material are located, these holes are filled by local deposition of the refractory material, using a vapor phase deposition technique, followed by a sinter, and a machining or grinding operation is carried out in order to remove material deposited in excess relative to the rest of the surface of the initial target coating.
United States Patent Application Publication No. 2011/0211676 (incorporated by reference) describes a method for repairing anodes, in which damaged sections of the target coating are removed, refractory material is deposited in the form of a powder, and this powder is sintered and a machining or grinding operation is carried out in order to remove excess deposited material.
The methods described in the above documents are not entirely satisfactory because the repaired sections are fragile.
U.S. Pat. No. 8,428,222 and United States Patent Application Publication No. 2011/0007872 (both incorporated by reference) describe a method for repairing anodes in which an annular portion of the disc, which portion is equipped with a target coating made of a refractory material, is removed and replaced by a new portion equipped with a new target coating, this new portion being brazed, soldered or welded to the disc.
This method requires the disc to be worked and positioning the added new portion poses problems.
The aim of the present invention is to improve considerably the properties of repaired anodes.